Convivo Technologies

OUTDOOR INTRUDER SYSTEM

These types of sensors would be found most of the time mounted on fences or installed on the perimeter of the protected area.

Vibration (shaker) or inertia sensors:

These devices are mounted on barriers and are used primarily to detect an attack on the structure itself. The technology relies on an unstable mechanical configuration that forms part of the electrical circuit. When movement or vibration occurs, the unstable portion of the circuit moves and breaks the current flow, which produces an alarm. The technology of the devices varies and can be sensitive to different levels of vibration. The medium transmitting the vibration must be correctly selected for the specific sensor as they are best suited to different types of structures and configurations.

More sophisticated sensors use piezo-electric components rather than mechanical circuits, which can be tuned to be extremely sensitive to vibration. These sensors are more durable and more resistant to tampering.

Passive magnetic field detection:

This buried security system is based on the Magnetic Anomaly Detection principle of operation. The system uses an electromagnetic field generator powering with two wires running in parallel. Both wires run along the perimeter and are usually installed about 5 inches apart on top of a wall or about foot buried in the ground. The wires are connected to a signal processor which analyzes any change in the magnetic field.

This kind of buried security system sensor cable could be buried on the top of almost any kind of wall to provide a regular wall detection ability or be buried in the ground.

E-field:

This proximity system can be installed on building perimeters, fences, and walls. It also has the ability to be installed free standing on dedicated poles. The system uses an electromagnetic field generator powering one wire, with another sensing wire running parallel to it. Both wires run along the perimeter and are usually installed about 800 millimeters apart. The sensing wire is connected to a signal processor that analyses:

These items define the characteristics of an intruder and when all three are detected simultaneously, an alarm signal is generated.

The barrier can provide protection from the ground to about 4 meters of altitude. It is usually configured in zones of about 200 metre lengths depending on the number of sensor wires installed.

Microwave barriers:

The operation of a microwave barrier is very simple. This type of device produces an electromagnetic beam using high frequency waves that pass from the transmitter to the receiver, creating an invisible but sensitive wall of protection. When the receiver detects a difference of condition within the beam (and hence a possible intrusion), the system begins a detailed analysis of the situation. If the system considers the signal a real intrusion, it provides an alarm signal that can be treated in analog or digital form.

Micro phonic systems

Micro phonic based systems vary in design but each is generally based on the detection of an intruder attempting to cut or climb over a chain wire fence. Usually the micro phonic detection systems are installed as sensor cables attached to rigid chain wire fences; however some specialized versions of these systems can also be installed as buried systems underground. Depending on the version selected, it can be sensitive to different levels of noise or vibration. The system is based on coaxial or electro-magnetic sensor cable with the controller having the ability to differentiate between signals from the cable or chain wire being cut, an intruder climbing the fence, or bad weather conditions.

The systems are designed to detect and analyze incoming electronic signals received from the sensor cable, and then to generate alarms from signals which exceed preset conditions. The systems have adjustable electronics to permit installers to change the sensitivity of the alarm detectors to the suit specific environmental conditions. The tuning of the system is usually accomplished during commissioning of the detection devices.

Taut wire fence systems:

A taut wire perimeter security system is basically an independent screen of tensioned tripwires usually mounted on a fence or wall. Alternatively, the screen can be made so thick that there is no need for a supporting chainwire fence. These systems are designed to detect any physical attempt to penetrate the barrier. Taut wire systems can operate with a variety of switches or detectors that sense movement at each end of the tensioned wires. These switches or detectors can be a simple mechanical contact, static force transducer or an electronic strain gauge. Unwanted alarms caused by animals and birds can be avoided by adjusting the sensors to ignore objects that exert small amounts of pressure on the wires. It should be noted that this type of system is vulnerable to intruders digging under the fence. A concrete footing directly below the fence is installed to prevent this type of attack.

Fiber optic cable:

A fiber-optic cable can be used to detect intruders by measuring the difference in the amount of light sent through the fiber core. If the cable is disturbed, light will ‘leak’ out and the receiver unit will detect a difference in the amount of light received. The cable can be attached directly to a chain wire fence or bonded into a barbed steel tape that is used to protect the tops of walls and fences. This type of barbed tape provides a good physical deterrent as well as giving an immediate alarm if the tape is cut or severely distorted. Other type’s works on the detection of change in polarization which is caused by fiber position change.

H-field:

This system employs an electro-magnetic field disturbance principle based on two unshielded (or ‘leaky’) coaxial cables buried about 10–15 cm deep and located at about 2.1 meters apart. The transmitter emits continuous Radio Frequency (RF) energy along one cable and the energy is received by the other cable. When the change in field strength weakens due to the presence of an object and reaches a pre-set lower threshold, an alarm condition is generated. The system is unobtrusive when it has been installed correctly, however care must be taken to ensure the surrounding soil offers good drainage in order to reduce nuisance alarms.